The invention relates to a flow control device for use with flowing liquids to monitor pressure during blood pressure measurements. Flow controllers of this type are known, for example, from DE Patent No. 30 23 345 or U.S. Pat. No. 4,341,224.
In general, during continuous intravasal pressure measurements, care must be taken that no blood coagulation occurs at the tip of the needle. This is achieved by producing continuous flushing. The needle is kept open by the flow of a fluid from a pressurized flushing fluid container and dispensed by the flow control device. The quantity of flushing fluid normally flowing is determined by a capillary bore and is commonly in the range of 3-6 ml/hour.
To prevent both a hazard to the patient and falsification of the results, the entire measuring system must be absolutely free of air bubbles, i.e., it must be ble of air before being connected to the patient. This is achieved by providing for a separate closable passage for the flushing fluid which has a considerable larger cross-sectional opening than has the capillary bore. As long as this closable passage is open, the flushing fluid flows through the passage which has a larger cross-section and thus fills the entire system in a short time. After the passage is closed, however, only the amount of flushing fluid which can pass through the capillary bore enters the system. In the flow control device described in DE Patent No. 30 23 435, the valve body which closes the passage is sealed by an O-ring with respect to a valve seat in the housing when in its inactive position. The capillary bore is contained in an insert within the valve body which has a passage upstream of the capillary bore in fluid flow communication with the inlet of the device.
A separate spring urges the valve body into its closed position. The valve is opened when the valve body is displaced against the force of that spring.
A similar flow control device, is shown in U.S. Pat. No. 4,497,468 and U.S. Pat. No. 4,291,702 in which the valve body is also disposed opposite a valve seat in the housing.
U.S. Pat. No. 3,675,891 also shows a similar flow control device in which the closable passage having the greater crossection for the capillary bore is disposed in parallel with the bore, serving as a bypass. Here too, to close the passage, a valve body is resiliently pressed against a valve seat in the housing. To open the passage for rapid flushing, the valve body must be raised from the valve seat against the force of the valve body acting as a spring, as in the previous examples.
Generally, it should be noted that the known flow control devices as well as those according to the present invention are intended for a single use only. Thus, they must be capable of being manufactured cost effectively but yet must function perfectly, making great demands on the tightness of the valve seat of the closable passage.
These demands have not as yet been met satisfactorily in the described state of the art. The known devices are generally composed of many individual parts, some of which are difficult to make and for a single use device are still too costly.